The invention relates to a method of accelerating hardening of thermosetting resin and a device therefor. More specifically, the invention relates to a method of accelerating hardening of thermosetting resin and a device therefor whereby it is possible, when thermosetting resin is to be hardened, to activate heat rays whose wavelengths are converted to levels which can be easily absorbed by the resin to be heated, such that the resin is uniformly heated.
It is common knowledge that as regards unhardened thermosetting resin, in order to shorten hardening time for purposes like improvement of hardening speed, such measures are taken as adding a hardening accelerator in advance and raising hardening temperature.
Incidentally, in the event that there is a danger of resin performance being affected by the above-mentioned measures, namely, preliminary addition of a hardening accelerator and raising of hardening temperature, then these measures cannot be taken, thus presenting a problem.
For example, high transparency, shape stability, and electrical capability regarding semiconductors are required in the case of epoxy resin for sealing LEDs, since light emitted from light-emitting diodes is radiated through epoxy resin, and therefore there is a limit to measures such as raising hardening temperature and using a hardening accelerator like Class III amine and triphenyl phosphine.
The object of the present invention, which was made by paying attention to the above-mentioned problem, is to provide a method of accelerating hardening of thermosetting resin and a device therefor whereby hardening time can be rendered much shorter than in the case of the prior art.
The method of accelerating hardening of thermosetting resin as set forth in the invention with the aim of achieving the above-mentioned object is such that when unhardened thermosetting resin is to be disposed in an atmosphere having a specified temperature for the purpose of hardening, a ceramic plasma spraying plane is formed in at least one portion in the above-mentioned atmosphere whose temperature is maintained at a specified level and in which the above-mentioned resin is disposed, thereby causing convective heat existing in the above-mentioned atmosphere having the specified temperature to be thermally converted into far infrared radiant heat radiation from the ceramic plasma spraying plane mentioned above.
As regards the above-mentioned atmosphere having the specified temperature, it is desirable that hot air be circulated by means of a device such as a blower for the purpose of uniforming temperatures. Furthermore, the fact that the above-mentioned resin is disposed in the above-mentioned atmosphere having the specified temperature signifies that the above-mentioned resin is exposed to an atmosphere having a temperature suited for the hardening of the above-mentioned resin. By way of a means for maintaining the temperature of the above-mentioned atmosphere at the specified level, air having an elevated temperature may be circulated between the above-mentioned unhardened thermosetting resin and a heat generator disposed outside or inside a furnace, and moreover, the heating value of the above-mentioned heat generator may be control led such that the temperature of the above-mentioned air is maintained at the specified level. There are no specific restrictions as to the area of the ceramic plasma spraying plane to be disposed around the resin to be hardened, but the larger the area is, the more preferable it is. Furthermore, as regards ceramic plasma spraying, any heretofore used conventional method may be used.
Thermosetting resins that may be applied to the present invention include, for example, not only epoxy resins like bisphenol type epoxy resin but also amino resins such as phenol resin, urea resin, and melamine resin; general-purpose thermosetting resins like unsaturated polyester resin and phthalic acid base resin; and various other thermosetting resins.
There are no specific restrictions as to ceramics that may be used. It is permissible to use quartz based ceramics such as alumina, chromium oxide, and silica sand; various other ceramics including titania; and appropriate mixtures of the above-mentioned ceramics.
There are no specific restrictions as to the grain size of ceramic powder to be subjected to plasma spraying. The preferable grain size depends on types of resins to be hardened. In the case of epoxy resin, it is preferable for the grain size to be between approximately 5 and 11 xcexcm. Likewise, there are no specific restrictions as to the plasma spray density. The preferable plasma spray density depends on types of resins to be hardened. In the case of epoxy resin, it is preferable for the density to be between approximately 5 and 20 g/m2. There are no specific restrictions as to the basal plate for subjecting ceramic to plasma spraying, but from the viewpoint of factors such as workability and prices, it is preferable to use a metal plate such as an aluminum plate.
Furthermore, the device for acceleration of hardening of thermosetting resin as set forth in the invention with the aim of achieving the above-mentioned object comprises a retainer for retaining unhardened thermosetting resin inside a furnace in which the above-mentioned thermosetting resin is hardened by maintaining the temperature at a specified level. At least one portion of the internal surface or the external surface of the above-mentioned retainer is used as a plasma spraying plane such that the above-mentioned plane is heated by the convective heat due to the atmospheric temperature inside the furnace, thereby causing far infrared radiation is radiated from the above-mentioned plane.
For the purpose of preventing the above-mentioned retainer from blocking the passage of the air that is circulated inside the furnace, it is preferable that a measure be taken such as providing the above-mentioned retainer with a plurality of openings or through holes.
It is stated above that according to the present invention, at least one portion of the retainer is used as the ceramic plasma spraying plane. However, it is permissible to use a portion of the internal wall of the above-mentioned furnace as the ceramic plasma spraying plane.
According to the present invention, it is considered that a ceramic plasma spraying plane is formed around thermosetting resin to be hardened, and that the functioning is such that the greatest possible quantity of wavelengths of heat rays inside the heated atmosphere around the above-mentioned thermosetting resin are converted into wavelengths that are easily absorbed by thermosetting resin. Therefore the functioning of the present invention is entirely different from that of the heretofore known blackening treatment whereby, for example, closely spaced cavities are provided on surfaces of the heat generator.
There are no specific restrictions as to fields of application of the present invention, which may be applied to resin in any field as long as unhardened thermosetting resin is hardened by heating. For example, the present invention may be applied to various fields such as sealing of semiconductors with epoxy resin; coating of semiconductor boards with epoxy resin; and insulation of coils, small coils in particular, of transformers and electric motors; as well as coating and hardening of objects with semi-molded prepolymers that are formed into filmy shapes.
As explained above, according to the method of accelerating hardening of thermosetting resin and the device therefor of the present invention, a ceramic plasma spraying plane is formed in an atmosphere having a temperature capable of hardening thermosetting resin, and therefore the quantity of far infrared radiation containing wavelengths that are easily absorbed by thermosetting resin increases, thus producing the effect of rendering hardening time far shorter than in the case of the prior art.